Batteries, or electrochemical cells, such as primary alkaline batteries or secondary lithium batteries, are commonly used electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized; the cathode contains or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When a battery is used as an electrical energy source in a device, electrical contacts are made with the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
Battery materials often are tested in a cylindrical battery form (e.g., AAA or AA battery), or in a button cell form. As an example, for a given cathode material, a button cell can include an anode (e.g., a zinc anode) and a potassium hydroxide solution, a separator paper, and a cathode containing a material of interest. During a discharge test, the anode is oxidized (e.g., to zinc hydroxide and oxide), the cathode material is reduced, and ionic transport occurs between the two electrodes and through the separator to maintain reaction stoichiometry. Usually, the cathode is mixed with a conductive aid such as graphite or carbon black to enhance discharge efficiency. Relatively large amounts of electrode active materials, numerous electrode preparation steps, and many cell components and assembly hardware are often used to make the test battery. Numerous factors can influence the data obtained from the discharge test. For example, the electrolyte resistance, material processing, amount of conductive aid (e.g., graphite), and contact resistance can all affect the accuracy of the test results.